That didn't work. Went through it, started download, now 'windows update standalone installer' has been searching for updates....... for AN HOUR.
What are you using to update? the CC Desktop app or did you click Update from the Lightroom Help menu?
Have you tried to obtain 6.8 from New Adobe Lightroom 6 (CC) Direct Download Links – Free Trials | ProDesignTools and use that to update?
I forgot to say...
As you said that you did not sign out, no problem there: if you are on Serial number and you run out of installations, just call Support to solve the issue; if you are in subscription, there's no real need to sign out.
You don't loose preferences when you reinstall from scratch, as they are stored in your user directory.
In case you have to wipe all of your disk (WHY?), just save the directory C:\Users\[user name]\AppData\Roaming\Adobe\Lightroom .
I am not cc. And it says light room 6 serial number no longer has phone support. I'd go to cc but I'm retired on social security and I can't justify that monthly/yearly fee when this is just a hobby. I have have not had a change to go at another reload again. I will try again later this week.
You should have no issue reinstalling on your existing computer.
Nevertheless, if you have to contact the Support in case of Activation issues, you have the chat:
go to Contact Customer Care (this is the UK one, but you should go to the one corresponding to your country)
click Download, installing, setting up
click Licensing and activation
click Still need help? Contact us.